No Tremolo on SF Twin Reverb

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JalfreziJalfrezi Frets: 55
I have a Twin Reverb that I rather like, but the tremolo has never worked.  I didn't have a footswitch until yesterday though, so wondered if that was the issue.  However I now have a footswitch and still no tremelo.

So, I'm about to pull the chassis and start trying to find the fault, I suspect that the LDR roach is dead, as the amp is so old, but does anyone know how to test the roach to prove/disprove that this is the faulty component?
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Comments

  • ICBMICBM Frets: 71963
    Have a look at it in a darkened room. If you can see the neon flashing (the opposite end from the controls) and the trem is still not working, it’s dead. If you can’t see the neon flashing the oscillator circuit is most likely faulty - if it’s not the valve, the three phase shift caps sometimes fail, or the cathode bypass cap. It’s very rare for the neon itself to go.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • JalfreziJalfrezi Frets: 55
    edited May 2019
    Thanks, I'll give that a go.  BTW, I swapped out the Trem valve earlier today, so seems like it's not the valve.
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  • jpfampsjpfamps Frets: 2723
    ICBM said:
    Have a look at it in a darkened room. If you can see the neon flashing (the opposite end from the controls) and the trem is still not working, it’s dead. If you can’t see the neon flashing the oscillator circuit is most likely faulty - if it’s not the valve, the three phase shift caps sometimes fail, or the cathode bypass cap. It’s very rare for the neon itself to go.
    I have seen a few neons where the inside of the bulb has silvered to the extent not enough light is incident on the LDR for the trem to work.

    It is usually the LDR that fails in the optocoupler though.
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  • JohnPerryJohnPerry Frets: 1616
    apologies for thread hijack. I have a 1971 DR that the trem only works on once you clout the top of the amp with the palm of your hand. Makes a little click, then works a treat. Every single time. Done it for years. What fault does that sound like - anyone know?

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  • ICBMICBM Frets: 71963
    JohnPerry said:
    apologies for thread hijack. I have a 1971 DR that the trem only works on once you clout the top of the amp with the palm of your hand. Makes a little click, then works a treat. Every single time. Done it for years. What fault does that sound like - anyone know?
    A cracked solder joint in the trem circuit.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • JohnPerryJohnPerry Frets: 1616
    Thanks John. I will have a look and see if it's visible

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  • earwighoneyearwighoney Frets: 3491
    ICBM said:
    JohnPerry said:
    apologies for thread hijack. I have a 1971 DR that the trem only works on once you clout the top of the amp with the palm of your hand. Makes a little click, then works a treat. Every single time. Done it for years. What fault does that sound like - anyone know?
    A cracked solder joint in the trem circuit.
    The LOL was from me, as that's some black belt diagnostics from ICBM. 

    I'm never ceased to be amazed by his insights. 
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  • JalfreziJalfrezi Frets: 55
    A new roach fixed this, whilst I had the chassis out, I took a snap of the guts, in the hope that an amp guru can point out any urgent, or critical faults (e.g. the death cap...).  Post HERE
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  • JalfreziJalfrezi Frets: 55
    Just too close this one, i replaced the roach today, and I now have a tremolo!

    I've snapped a pic of the guts, in the hope that someone more knowledgable can point out anything that should be addressed.  The filter caps in the doghouse we replaced quite recently.  Anyway, new post here



    my trading feedback HERE
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  • JalfreziJalfrezi Frets: 55
    Just too close this one, i replaced the roach today, and I now have a tremolo!

    I've snapped a pic of the guts, in the hope that someone more knowledgable can point out anything that should be addressed.  The filter caps in the doghouse we replaced quite recently.  Anyway, new post here



    my trading feedback HERE
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
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